Conventional positioning systems, such as Global Position Satellite (GPS) receivers, are increasingly being integrated into battery operated user equipment (i.e., personal digital assistants and cellular telephones). The positioning systems calculate the locations of the user equipment based on signals received from the GPS satellites. The locations are used to provide applications and services for the benefit of the users, for example enabling parents to track children, to deliver location-based information and advertising or to assist with navigation.
Due to power consumption constraints in battery operated equipment, conventional positioning systems are normally only enabled on demand from the user. Hence, the applications and services can only be delivered following an explicit request from the user to establish a current location. In contrast, the utility of the positioning features and the applications would be greatly enhanced if the receiver is capable of continuously tracking the location of the equipment. In such cases, applications that use the location information can proactively deliver location-based services to the user without waiting for any prior input from the user. To enable continuous use, however, the power consumption of both the positioning system that tracks the current user location and the applications that deliver services based on the current location should to be reduced to an absolute minimum.